Tim J. Grandjean, Jaco C. de Smit, Jim van Belzen, Jasper Dijkstra, Chiu H. Cheng, Joana van Nieuwkoop, Madelief Doeleman, Lennart van IJzerloo, Wietse I. van de Lageweg, Tjeerd J. Bouma
Salt marshes provide essential ecosystem services, but in engineered, sediment-rich estuaries, rapid vertical accretion often leads to a successional trap. This results in climax-dominated, species-poor, elevated salt marshes characterised by reduced inundation and the loss of pioneer habitats. We investigated topsoil removal (30–40 cm) as an ecological engineering strategy to restore habitat heterogeneity in a constrained salt marsh in the Western Scheldt (NL). Over four years, we integrated field monitoring of sedimentation, hydrodynamics and vegetation with wave modelling under 1:10,000-year storm conditions. Results demonstrate that lowering the marsh platform maintained flood safety levels equivalent to the pre-intervention baseline, as the seaward marsh fringe primarily governs wave attenuation. Post-intervention monitoring revealed high vertical accretion rates (1–6 cm yr −1 ), yet the aimed restored pioneer stage was transient. Within four years, Salicornia spp. were significantly replaced by high-successional Elymus repens . We attribute this successional bypass to restricted tidal drainage and a 10% reduction in peak water levels compared to reference elevations. While topsoil removal effectively rejuvenates mature marshes, we conclude that elevation reduction alone is insufficient for long-term biodiversity gains without enhancing tidal connectivity.